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    <title>Document</title>
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<script>
    function zhuhuan(str1){
        var str=str1.split('')
        for(let i=0;i<str.length;i++){
            if(str[i].charCodeAt()>=65&&str[i].charCodeAt()<=90){
                str[i]=str[i].toLowerCase()
            }else{
                str[i]=str[i].toUpperCase()

            }
        }
        console.log(str.join(''));
    }
    zhuhuan("HelloWorld")
</script>